It is known to produce aqueous solutions of ATS by reacting a solution of ammonium sulphite with sulphur in liquid form or with sulphides or polysulphides in aqueous solution as described in Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition, 1997, vol 24, page 62 and in U.S. Pat. Nos. 2,412,607; 3,524,724 and 4,478,807.
It is furthermore known from U.S. Pat. No. 3,431,070 to produce ATS in a continuous process from gaseous feed streams comprising H2S, NH3 and SO2. By the process of this invention ATS and sulphur is produced from a first feed gas stream comprising H2S and NH3 and a second feed gas stream comprising SO2 in three absorption steps. In a first absorber, NH3 and H2S are separated in a H2S off-gas stream and an NH3-rich solution of ATS. The main part of the solution is passed to a second absorber, in which it is contacted with the SO2-rich feed gas stream under formation of an off-gas that is vented and a solution rich in ATS and ammonium sulphites, which in a third absorber is contacted with the H2S-gas from the first absorber and, optionally, with additional H2S. After removal of sulphur being formed in the third absorber, the major part of the ATS-solution formed in the third absorber is recycled to the first absorber, while a minor part is mixed with a fraction of the NH3-rich solution of ATS formed in the first absorber forming the product solution of ATS.
There are three major disadvantages of this process: Elementary sulphur is formed in the third absorber and must be separated from the solution, the off-gas vented from the third absorber has a high concentration of H2S and the process is complicated with three integrated absorption steps.
It is also known from EP 0 928 774 A1 to produce an aqueous solution of ATS from gaseous feed streams comprising NH3, H2S and possibly SO2. By the process of this patent, a concentrated solution of ammonium hydrogen sulphite (AHS) is produced from NH3 and SO2 in a first absorption step comprising one or two absorbers in series. Said solution is contacted in a second absorption step with a gaseous mixture of H2S and NH3 forming the product solution of ATS.
The major disadvantage of this process is that it requires import of NH3 for the process.
Furthermore, a process is known from Danish Patent No. 174407, wherein ATS is produced by using only the NH3 contained in the SWS-gas stream as the NH3 source for ATS-production.
In said process a first feed stream, typically SWS-gas, comprising more than 0.33 mole H2S per mole of NH3 is contacted with a stream of sulphite solution in line 18 in the drawing FIG. 1 and FIG. 2 in said patent application in a reactor A1 for formation of ATS. However, experiments have shown that the presence of excess H2S for the formation of ATS from sulphites in the reactor will lead to the presence of free sulphide in the product solution (line 12), part of which is recycled (line 17) to the SO2 absorber (A2), in which the sulphide will be decomposed to give H2S in the absorber effluent gas (line 19). Furthermore, the large recycle of solution (line 13) to the SO2 absorber and back to the reactor (lines 17–18) is also a disadvantage of the process.
The objective of this invention is to establish an improved process for the production of ATS in which over 99.9% of all sulphur and all NH3 in the feed streams are recovered as ATS without any of the above mentioned disadvantages.